You graphics Card is a ATI XT1650 Pro 512MB AGP card. THe Dell PSU is very underated and low at 250w.
Your problem is replacing the AGP card with something that has more kick and there isn't much arround for this now as PCI Express has replaced the AGP slot's on motherboards.
I agree you need a bigger more humph AGP Card and if you can find one then that is one thing sorted. The PSU I would recomend something about 500w - 600w to be on the safe side. Also making sure any replacment AGP card if it has its onw Power Conector like a 4pin Power required from the PSU itself. So matching PSU to the AGP card.
At the end of the day. you will be limited and I would consider a replacment machine depending on your funding or sourcing a second hand AGP card of Ebay.
Have you seen any AGP cards you were looking at, maybe post here and we can have a look.